Valley Fog

This was the view from my garden yesterday and one of the geekiest things about living in Calderdale with all its hills and valleys.

Often we wake up in Spring and Autumn and it looks like the valley below has filled with fog.

So what is Valley Fog (or mountain fog, depending on your perspective I suppose!)?

Overnight as the air cools it becomes more dense and will sink to the dip in the bottom of the valley, if it gets cold enough for the water droplets in the air to condense, fog will form and sit in the valley until the air starts to warm up and rise.

Valley fog is really thick and we often have to drive through it on the school run which gives that very strange sensation you get when you fly through the clouds on a plane - except at the end, you aren't on holiday, you're at school instead...In really hilly areas, valley fog is really dense and dramatic but you only need a slight dip for this to happen and you may notice your visibility getting slightly worse if you drive over a dip in the road early on a chilly morning.

This is a really visual link if you are teaching about weather systems, the water cycle and states of matter.